Vacuum tube seal and method



Feb. 2, 1943. c. v. L ITTON .VACUUM TUBE SEAL AND METHOD Filed Feb. 6,1942 Fmzz IN VEN TOR. CHARLES l/., L/TTO/V TTOHNE Y.

Patented Feb. 2, 1943 VACUUM TUBE SEAL AND METHOD Charles V. Litton,Redwood City, Calif., assignor to International Standard ElectricCorporation, New York, N. Y., a corporation of Delaware ApplicationFebruary 6, 1942, Serial No. 429,74

6 Claims.

This invention relates to electron discharge devices and a method ofmaking them, and has for its principal object to facilitate the assemblyof vacuum tubes.

Vacuum tubes have heretofore been made with a glass envelope for theevacuated vessel inside of which the electrodes have been supported bysuitable means, either by extending directly through the glass wall orby mounting on metal sections sealed between sections of the glass. Thefinal step in completing the tube envelope has been the creation of thefinal glass seal with the electrodes inside the envelope, after whichthe vessel has been evacuated in a well-known manner. The making of thefinal glass seal has presented some difiiculty, particularly in verysmall tubes such as those commonly used at ultra high frequency.

In accordance with this invention, the assembly of the tube isfacilitated by providing a metallic envelope section in twocomplementary parts, joining each part to its adjacent Vitreous sectionand then sealing the metallic parts together. By using this invention avacuum tube can be completely assembled with all its electrodes attachedto their supporting members and the final seal can then be made as ametal-tometal seal between two metal parts.

A feature of the construction is an arrangement of the complementarymetal seal members such that the location of the metal seal portion isaway from the glass seals, and at a position where it can easily beworked on, and is separated from the glass by a thin metal section. Arelated feature is the provision of a supporting construction to preventany appreciable yielding of the thin parts of the complementary metalseal members when the tube is evacuated.

The invention will be understood from the detailed description and theaccompanying drawing, of which Fig. 1 illustrates in longitudinalsection a vacuum tube made with a metal seal in accordance with thisinvention,

Fig. 2 is a cross section of the metal seal means taken at arrows 22 ofFig. 1; and

Fig. 3 is a section looking in the direction of arrows 3-3 of Fig. 1.

Fig. 1 illustrates a vacuum tube comprising glass envelope sections H],II and I2, and a metal section i3, so that the envelope is in thegeneral form'of a cylinder closed at both ends. The envelope of the tubeis completed by complementary metallic seal members 14 and I5,preferably copper, forming a section of the envel e. The

shape of the tube and its electrodes is not of spe cial importance in sofar as the present invention is concerned, and is shown for exemplarypurposes only. The tube is shown in a conventionalform with a cathode inthe form of a filament [6 connected at one end to a rod terminal I!passing through the glass stem i8, and connected at the other end to thesimilar filament terminal lead 19 passing through the stem. Around thefilament is a control electrode or grid shown in the form of a wirehelix 20 supported on rods 2| which'are carried by the inner surface ofmember I4. The metallic section I3 is used as an anode in thearrangement shown.

The assembling of such a tube is greatly facilitated in accordance withthis invention by the use of the metal members 14 and I5, particularlywhen the tube is of very small size. End views of members [4 and I5 areillustrated in Figs. 2 and 3, respectively. Member 15 comprises anannular body portion in the form of a ring 22 tapering to a feather edgeat 23 adapted to be readily sealed to the glass section [0, andrelatively thin annular disc portion 24 extending radially outwardlyfrom the ring 22. The outer portion of 24 is bent over to form a flange25 which may be cylindrical as shown.

The complementary member M likewise comprises a body portion in the formof a ring 26 of substantially the same diameter as ring 22, andterminating in a feather edge 21 similar to edge 23 for sealing with theglass section II. A thin annular disc portion 28 extends radially fromthe side of the ring portion 26 at a position somewhat spaced from disc24, and the disc 28 is bent over to form a flange 29 which correspondsand contacts with the circumferential surface of flange 2.5. .Thearrangement might, if desired, be made by placing part 29 outside ofpart 25, instead of inside as shown; or if desired, the parts 25 and 29might have some other shape than cylindrical flanges, so long as thereare provided continuous complementary sealing surfaces around theoutside of the envelope. The ring portion 26 is provided with radialslots 27 providing solid abutting portions 26a which lie against thefiat surface 32 of member 15; and the slots provide communication fromthe an.- nular cavity 3i formed between members 24 and 28, to the mainportion of the vessel. The bentover flanges 25 and 29 are sealedtogether as by brazing.

The use of the seal members [4 and I5 provide a very easy methodofassembling the tube as the last step in the completion of the tubeenvelope may be the metal sealing of flanges 25 and 29, which are ofrelatively large diameter and removed from the rest of the tube. Thus,the filament and its leads may be sealed through the glass stem 18, andthe section ll) of the glass may be sealed to the member l5; andlikewise any other desired attachments or seals may be made at this partof the tube. Likewise, glass section [2 may be sealed to metal sectionl3 and metal sections 53 and M may be sealed to the glass section II,with the grid fastened in place by the attachment of grid supports 2| tomember 14; and any other desired attachments may be made to this part ofthe tube. Then the complementary members Hi and brought together intothe position of Fig. 1 and sealed as by brazing together members 25 and29 to complete the tube. brazing operation will not injure the glassseals at feather edges 23 and 21 because of the distance of flanges 25and 29 from the glass, and the thinness of the disc portions 24 and 28,Which will not rapidly conduct heat to the glass.

Then the tube may be evacuated as by attaching a vacuum pump in awell-known manner at the position 30 of glass section [2. The gases andair are completely evacuated from the tube, and also from the cavity 3|formed between discs 28 and 24 through the radial slots 21. Except forthe presence of abutments 26a against surface 32 the thinness of walls24 and 28 might tend to make these walls collapse under the pressure dueto the vacuum. Such collapse is prevented, however, by the abutments 26abecause these abutments are located at positions of great strength ofthe member 14, and are flat against the solid portion 22 of member l5,external air pressure on 24 and 23 tending to press the parts 22 and 26atogether.

By the use of this invention the assembly of the tube is greatlyfacilitated especially when the size ,of the tube is small, for it ismuch easier.

to make the metal seal around the relatively large diameter sealing.flanges than to make the final seal of glass of much smaller diameter.Moreover, in small tubes it is difficult to prevent softening of theglass envelope while making conventional seals. The location of themetal seal at such a distance from the glass beyond the relatively heavymass of members 14 and I5 and separated from these members by the thindiscs protects the glass from the heat used in making the metal seal andpermits high temperatures to be used on the metal without injury to theglass.

It will be understood that the invention is not limited to theparticular arrangement shown, which is given for the purpose ofillustration, but extends to other arrangements within the scope of thefollowing claims. It is furthermore not required that an electrode beattached to thecomplementary seal members. 7

What is claimed is:

1. In a vacuum tube having vitreous sections in the tube envelope, meansfor joining two of said vitreous sections together comprising a metallicmember sealed to each of said sections, each of said metallic membershaving a body portion adjacent the vitreous section, and a thin may be.

The heat required for such disc-like portion extending outwardly fromthe body portion, said disc-like portions having contacting surfaceswhich are sealed to each other, one of the body portions havingabutments which lie against the other body portion and having passagesbetween said abutments leading from the evacuated vessel to the cavitybetween said disclike portions.

2. A vacuum tube comprising a pair of complementary tubular metalmembers adapted to abut each other, reinforcing annular members formedat the abutting edges of said tubes to resist air pressure, a relativelythin disc-like metalmember formed coaxially on each of said annularmembers, and a seal connecting the outer edges of said disc-likemembers.

3. A vacuum tube comprising a pair of tubular metal members eachterminating in a metal ring of substantially greater thickness than thetube walls, a relatively thin metal disc formed coaxially on the outersurface of each ring, and a seal connecting said discs in an areaadjacent to the outer edges thereof.

4. Means for sealing two sections of a vacuum tube comprising a pair oftubular metal members terminating in complementary metal rings ofsubstantially greater thickness than the walls of said tubular members,a flange of relatively thin metal projecting from the outer surface ofeach ring, and a seal connecting said flanges near the outer edgesthereof the metal mass of said rings serving to dissipate heat conductedthereto by said flanges during the sealing operation and also toreinforce said'flanges and said tubular members to resist the effects ofexternal air pres-v sure.

5. Means for sealing two sections of a vacuum tube in which each sectionterminates in a tubular metal member having edges adapted to abut eachother, a metal ring of substantially greater thickness than the walls ofsaid tubular members formed at. the abutting edge of each tubularmember, a flange of relatively thin metal formed on the outer surface ofeach ring, a seal connecting said flanges near the outer edges thereofand air passages formed between the. adjacent surfaces of said ringsconnecting the interior of said tubular members and the adjacentsurfaces of said flanges.

6. Means for sealing two sections of a vacuum tube in which each sectionterminates in a tubular metal member having edges adapted to abut eachother, a metal ring of substantially greater thickness than the walls ofsaid tubular members, formed at the abutting edge of each tubularmember, a flange of relatively thin metal formed on the outer surface ofeach ring, said flanges being disposed so that they are in spacedrelationship to each other, air channel means connecting'the interior ofsaid tubular members with the space between said flanges, means disposedat the outer edges thereof to maintain the spaced relationship betweensaidflanges and a seal sealing said flanges together at theirperipheries, the arrangement being such that external air pressure onthe surface of said flanges tends to press the two tube sectionstogether.

CHARLES ..V. LITTON.

